The present invention relates generally to lighting devices, and more particularly to an organic light emitting diode.
Electroluminescent (EL) devices have been known for more than 60 years. A schematic illustration of an electroluminescent device 1 is shown in FIG. 1. The EL device 1 contains an inorganic phosphor layer 3, such as ZnS, doped with activator ions, such as Mn. The phosphor layer 3 is sandwiched between two insulating layers 5 and 6. A cathode 7 and an anode 8 are located on the outer sides of the respective insulating layers 5, 6.
EL emission occurs in the following way. Above a threshold voltage applied between the anode 8 and the cathode 7, electrons are injected from the interface states between the phosphor layer 3 and the insulating layers 5, 6 by high field assisted tunneling. The injected electrons (illustrated by arrows) excite the activators in the phosphor layer 3 through an impact excitation mechanism. The excited activators then make radiative transitions to the ground state and emit light. The electrons travel in the conduction band from the interface between the phosphor layer 3 and the insulating layer 5 to the interface between layers 3 and 6, where they are trapped and cause polarization. When the polarity of the ac voltage wave is reversed, the same process takes place in the opposite direction in the phosphor layer. Thus, light emission takes place from the activator ions in the inorganic phosphor, due to the collisions with electrons travelling in the electronic bands of the phosphor under an applied electric field.
Flexible fiber electroluminescent light sources are known in the art, as set forth, for example in U.S. Pat. Nos. 6,074,071, 5,485,355 and 5,876,863. However, these EL devices are unable to achieve sufficient brightness for many lighting applications.
Chemiluminescent fiber light sources are also known. These devices emit light when they are twisted to combine two chemicals contained in the fiber. The chemical reaction between the chemicals produces light while the chemical reaction proceeds for a few hours. However, these prior art chemiluminescent fiber light sources also lack sufficient brightness, and have a very short lifetimes, on the order of a few hours.
In contrast, organic light emitting devices (OLEDs) have only been known for about 10 years. These devices operate in a fundamentally different way from EL devices. FIG. 2 is a schematic illustration of an OLED 11. The OLED device 11 includes an organic radiation emitting layer 13 disposed between two electrodes, e.g., a cathode 17 and a light transmissive anode 18, formed on a flat sheet, light transmissive substrate 19. The organic radiation emitting layer 13 emits light upon application of a voltage across the anode and cathode. For example, the organic emitting layer 13 may comprise a polymer layer in direct contact with the cathode 17 and the anode 18. No insulating layers which prevent charge transfer from the electrodes to the organic layer are present between layers 13, 17 and 18. Upon the application of a voltage from a voltage source 14, electrons are directly injected into the organic layer 13 from the cathode 17, and holes are directly injected into the organic layer 13 from the anode 18. The electrons and the holes travel through the layer 13 until they recombine to form excited molecules or excitons. The excited molecules or excitons emit radiation (i.e., visible light or UV radiation) when they decay. Thus, the OLED 11 emits radiation (illustrated by the arrows in FIG. 2) by electron-hole recombination due to direct electron and hole injection into the radiation emitting layer, rather than by activator ion excitation by electrons, as in an EL device.
The OLED devices are much brighter than EL or chemiluminescent devices. However, the flat plate shaped OLED devices formed on flat sheet substrates are generally not flexible, as the EL or chemiluminescent devices. There have been attempts to attain a high degree of mechanical flexibility in an OLED. For example, U.S. Pat. No. 5,844,363 and an article in Volume 357, page 477 of the Jun. 11, 1992 issue of Nature describe an OLED device 11 formed on a flexible, light transmissive flat plastic PET sheet which is used as the substrate 19. However, the resulting OLED 11 has an impracticably short life due to water and/or oxygen permeation into the light emitting layer 13. Attempts have been made to add barrier layers, such as SiO2 and Si3N4, to the plastic film 19 to eliminate the water and/or oxygen permeation. However, the barrier layers have not led to long lived devices. Another approach is to fabricate the OLED 11 on a very thin glass sheet substrate 19 to impart moderate flexibility to the device. However, the thin glass sheet substrates are only moderately flexible and are not amenable to low cost, continuous processing. The present invention is directed to overcoming or at least reducing the problems set forth above.
In accordance with one aspect of the present invention, there is provided a fiber organic radiation emitting device comprising a fiber core having an outer first electrode, at least one organic radiation emitting layer positioned over an outer surface of the first electrode, and a radiation transmissive second electrode positioned over the organic radiation emitting layer.
In accordance with another aspect of the present invention, there is provided a flexible, fiber organic radiation emitting device, comprising a flexible elongated core member having an outer surface, a cathode having an inner surface surrounding the outer surface of the core member, at least one non-planar organic radiation emitting layer, having an inner surface surrounding and contacting an outer surface of the cathode, a radiation transmissive anode having an inner surface surrounding and contacting an outer surface of the at least one organic radiation emitting layer, a metal contact element having a first surface in contact with a first portion of an outer surface of the anode, and a power source electrically connected to the cathode and the metal contact element.
In accordance with another aspect of the present invention, there is provided a method of making a flexible organic radiation emitting device, comprising forming a core having an outer first electrode layer, depositing at least one organic radiation emitting layer around the first electrode layer, depositing a second electrode layer around the at least one organic radiation emitting layer, and electrically connecting a power source to the first and second electrode layers.
In accordance with another aspect of the present invention, there is provided a continuous method of making a flexible fiber organic radiation emitting device, comprising winding a flexible fiber core member having an outer first electrode layer from a first spool to a second spool, depositing at least one organic radiation emitting layer around the first electrode layer in a first deposition area, depositing a second electrode layer around the at least one organic radiation emitting layer in a second deposition area, unwinding the coated core from the second spool and separating the coated core into a plurality of flexible fiber sections, and electrically connecting a power source to the first and second electrodes on at least a first fiber section.
In accordance with another aspect of the present invention, there is provided an apparatus for continuous fabrication of a flexible fiber organic radiation emitting device, comprising first means for winding a flexible fiber core member containing an outer cathode layer to a second means, third means for depositing at least one organic radiation emitting layer around the cathode layer in a first deposition area, and fourth means for depositing a radiation transmissive anode layer around the at least one organic radiation emitting layer in a second deposition area.
In accordance with another aspect of the present invention, there is provided an apparatus for continuous fabrication of a flexible fiber organic radiation emitting device, comprising a first spool, a second spool, an organic layer deposition chamber, in which at least one organic radiation emitting layer is deposited around a first electrode layer, and a first electrode deposition chamber capable of coating plural sides of a fiber, in which a first electrode layer is deposited around the at least one organic radiation emitting layer.